A standard drill has a drill housing and a drive spindle centered on and rotatable about an axis, projecting axially outward from the housing, and having an outer end. A chuck element is fixed on the spindle outer end and an adjustment ring element is axially fixed but rotatable about the axis on the chuck element. One of the elements is formed with a plurality of axially forwardly open guide passages open axially rearward into the chamber and the other of the elements is formed with a screwthread centered on the axis. The elements are both rotatable about the axis relative to the formation. Respective jaws are displaceable in the passages between axially front and radially closely spaced positions and axially back and radially widely spaced positions and have teeth meshing with the screwthread. Thus rotation of the ring element in a forward direction on the chuck element displaces the jaws axially forward and radially inward and opposite rotation of the ring element in a reverse direction on the chuck element displaces the jaws axially backward and radially apart.
The main problem with this type of drill and chuck assembly, which is described in my U.S. Pat. Nos. 4,836,563 and 5,378,002 and in my German patent 3,437,792 is that the overall length of the chuck assembly is excessive. In order to accommodate the axial travel of the jaws, it is necessary to make the chuck fairly long which makes the drill harder to handle while adding nothing to its functionality. Since the chuck itself is normally a standard item that is installed on the drill body, there is little interrelationship between the two parts, that is one is not designed to go particularly with the other.